1. Field of the Invention
The present invention relates generally to the field of locks, and more specifically to a removable plug cylinder lock such as may be used in vending machine coin boxes.
2. Prior Art
Locks and removable plug cylinder locks are well known in prior art. These locks are used in vending machines, cash boxes, parking meters and the like. An excellent discussion of the nature of the coin box used in the machines is found in U.S. Pat. No. 3,871,284, issued on Mar. 18, 1975 to Krise, for a xe2x80x9cCoin Box and Lock Mechanismxe2x80x9d. As explained in the ""284 patent, a coin box is typically securely affixed inside a vending machine with an opening in the vending machine to allow access to the contents of the coin box. A metal plate covers the opening with an appropriate fastening mechanism that requires a special access tool. A smaller aperture located in the cover, designed to allow special access to the fastening mechanism, is blocked by a cylinder plug lock. The current invention relates to improvements in cylinder plug lock technology.
The cylinder plug lock includes a locking plug portion that slides in and out of a hollow cylinder portion. The cylinder portion is rigidly affixed to the cover plate. When the plug is properly aligned the cylinder, the plug may be secured and the plug key removed. A problem arises when inserting the plug because prior art devices have made it sometimes difficult to align the plug properly within the cylinder.
Prior art lacks a plug that easily and unmistakably seats into a position that easily allows the removal of the plug key without removing the plug as well. Stated slightly differently, prior art devices did not provide a foolproof way to inform the installer that the plug was properly aligned, so that the installer could then remove the key without also removing the plug. Often, when using prior art devices, the installer was left fumbling, sometimes in the dark and sometimes in extreme cold while wearing gloves, trying to get the plug rotationally and/or axially aligned correctly to complete installation of the plug into a locked and secured position.
One prior art method of aligning the plug is to use a xe2x80x9cc-clipxe2x80x9d or spring bar that attaches to the plug and installs into a groove when the plug is inserted into the cylinder. The clip/bar is initially compressed within the cylinder until it aligns with the groove in the inside diameter of the cylinder and then expands into the groove to hold the plug in place while the locking mechanism is actuated. The ease with which the user aligns the plug to the cylinder depends on the flexibility of the clip and the ability of the user to feel and/or hear the clip/bar snap into place. If the clip/bar is too rigid, it will be difficult to remove the plug after it is aligned and seated. If the clip/bar is too flexible, it is harder to know when the groove that aligns and seats the plug within the cylinder is engaged.
Another common prior art technology requires two keys for the lock. The first key operates the tumbler mechanism within the lock. The second key is slightly longer and moves a pin that releases the plug and allows it to be removed from the cylinder. The use of the two keys raises the inevitable possibility that at least one of the keys will be lost, rendering the lock useless.
Thus, a method and a device are needed that allow a plug to be easily, quickly and unmistakably aligned within a lock cylinder when inserting the plug into the lock cylinder. Further, such a device should not require two keys to operate.
Further features and advantages of the present invention will be appreciated by reviewing the following drawings and detailed description of the invention.
According to the present invention, a removable locking plug is easily inserted and/or removed from the cylinder portion of the locking mechanism. In the preferred embodiment, the plug is enclosed in a case hardened steel housing and contains a tumbler keyed locking mechanism. It has a key activated latch that extends and retracts radially from the sidewall of the plug housing. With the latch in the retracted position, the plug can fit snugly into the cylinder.
In the preferred embodiment, the cylinder has an inner flange at the rearward end. An alignment lug or pin extends radially inward from the wall at the inner flange. The plug has an alignment notch to receive the lug/pin when the plug is properly aligned within the cylinder. Cooperation between the alignment notch and the alignment pin acts to prevent rotational movement of the plug within the cylinder. When so aligned, the latch can be extended into a locking notch cut into the cylinder wall at the inner end, preventing the plug from both axial and rotational movement within the cylinder. The plug key may then be removed without removing the plug.